1. Field of the Invention
The present disclosure is related to a power supply controlling device, a power supply device, an image forming apparatus, and a power supply controlling method.
2. Description of the Related Art
Electrophotographic image forming apparatuses are configured to form an image on a recording medium by forming an electrostatic latent image on an image bearer uniformly charged, forming a toner image by developing the formed electrostatic latent image with toner, and transferring and fixing the formed toner image onto the recording medium.
Further, a technique is also known by which an image forming apparatus such as that described above uses a power supply device in which a direct-current power supply and an alternating-current power supply are connected in series so that it is possible to switch between transferring the image onto the recording medium by applying a direct-current voltage from the power supply device to a transfer unit and transferring the image onto the recording medium by applying a superimposed voltage obtained by superimposing a direct-current voltage and an alternating-current voltage together from the power supply device to a transfer unit.
When the recording medium has projections and recesses, although toner is transferred to the recesses less easily than to the projections, it is possible to improve the toner transfer efficiency by transferring the toner while using a superimposed voltage obtained by superimposing an alternating-current voltage. Thus, by using the image forming apparatus described above, it is possible to improve the quality of the image, even if the image is formed onto the recording medium having projections and recesses.
However, it should be noted that, in the power supply device described above, due to an influence of a bypass capacitor used for preventing the output of the alternating-current power supply from being routed into the direct-current power supply, it takes a longer period of time for the direct-current voltage output by the direct-current power supply to rise than in situations where the direct-current power supply is used alone.
To cope with this situation, US Patent Application Publication No. 2014/0265552, for example, proposes a technique by which an output of a direct-current voltage is started by exercising constant voltage control, and subsequently, the output of the direct-current voltage is realized by switching the controlling method to constant current control, so that it is possible to shorten the charging period of the electric charge into a bypass capacitor and to shorten the rising period of the direct-current voltage.
According to the conventional technique, however, the start of the constant current control is delayed by an influence of a residual electric charge remaining after the controlling method is switched from the constant voltage control to the constant current control. Consequently, there may be some situations where the direct current output from the power supply device becomes too low before the constant current control is started, and it may thus become impossible to cause the direct-current voltage to rise within an expected period of time.
In view of the circumstances described above, there is a need to provide a power supply controlling device, a power supply device, an image forming apparatus, and a power supply controlling method with which it is possible to cause the direct-current voltage to rise within the expected period of time, while shortening the rising period of the direct-current voltage.